Why do farther away objects appear smaller

  • Thread starter member 529879
  • Start date
In summary, the size of an object appears smaller as the distance between it and the observer increases due to the angle it subtends at the eye becoming smaller. This is a result of the brain coordinating the views from both eyes and estimating the distance to the object. This effect can also be seen in images taken with a single "eye" system. However, this apparent size can be increased by using optical systems such as tele-objectives or telescopes.
  • #1
member 529879
Why do objects that are farther away appear smaller. The moon for example looks small from earth, but I don't understand why.
 
Physics news on Phys.org
  • #2
It's geometry. The angle between two parts of an object gets smaller as the distance from them increases. You can draw a diagram.
 
  • #3
Scheuerf said:
Why do objects that are farther away appear smaller. The moon for example looks small from earth, but I don't understand why.

The apparent size of an object is (pretty much by definition) the angle that it subtends across our field of view. If you keep the size of the object constant while you increase the distance to the object, that angle gets smaller. Draw a few right triangles with the same length for one of the sides meeting and the right angle and different lengths for the other side meeting at the right angle, compare the angle opposite the fixed side, and you'll see this effect clearly.
 
  • #4
Or try this one:
Hold your hand in front of your face so that nearly everything in the background is obscured by it.
Most of your field of view sees your only your hand.
Now move your hand away to arm length - Now you can see more of what is in the background right?
Did your hand actually get smaller?, no, it just got further away.
 
Last edited:
  • #5
Scheuerf ; You asked: Why do objects that are farther away appear smaller. The moon for example looks small from earth, but I don't understand why.

Reference https://www.physicsforums.com/threads/why-do-farther-away-objects-appear-smaller.822290/

An object's apparent size{ visual angle in astronomy } is the angle it subtends at the eye. See Wikipedia, "visual angle" for drawing. Plain old geometry.The larger or closer the object, the bigger the angle and bigger the real though upside down image on the eye. Our brain's"computer" enhances and rights the image and ultimately uses past experience to give the perceived size. A close basketball appears bigger, a far basketball appears smaller. Our brain knows better most of the time. Perceived size is also affected by surrounding objects like the horizon.The brain is fooled. Notice how huge the moon or sun seems to get as it approaches the horizon. A rather striking effect.View the moon through a paper tube to eliminate peripheral cues and the size appears the same.
 
  • #6
Some say that objects, even people, actually shrink, the further they are. This is peripherally supported by the related theory: Out of Sight, Out of Mind.
 
Last edited:
  • Like
Likes Drakkith and jbstemp
  • #7
So if we had flat eyes and not lenses, then objects would appear to be the same size no matter ho far a way they were?
Surely this is possible to emulate with a CCD that had no lens to concentrate the light ?
 
  • #8
johnEHDS said:
So if we had flat eyes and not lenses, then objects would appear to be the same size no matter ho far a way they were? Surely this is possible to emulate with a CCD that had no lens to concentrate the light ?
You wouldn't see any objects at all.
 
  • #9
johnEHDS said:
So if we had flat eyes and not lenses, then objects would appear to be the same size no matter ho far a way they were?
Surely this is possible to emulate with a CCD that had no lens to concentrate the light ?
You'd need telecentric lens for it: http://www.lhup.edu/~dsimanek/3d/telecent.htm
 
  • #10
johnEHDS said:
So if we had flat eyes and not lenses, then objects would appear to be the same size no matter ho far a way they were?
Surely this is possible to emulate with a CCD that had no lens to concentrate the light ?
A bare sensor with no lens doesn't focus light to create an image.
 
  • #11
The reason that objects become smaller with radial or linear distance is because we have two eyes and view objects from each eye creating a triangle from the object to the location of each eye. The brain coordinates both views into a single image. The coordination of separate views creates as triangle that will show the exact rate of visual size reduction based on the distance from the object to the point where both eyes see the same object in perfect focus or it disappears from visible sight. This a simple but accurate explanation. I hope this helpful!
 
  • #12
Having two eyes and all that is related to the way our brain can estimate distance to objects and give us the sensation of 3D vision.

However, the size of distant objects is smaller even in images given by a single "eye" systems, like a photographic camera.
Similarly, the image of distant objects on the retina is indeed smaller and fewer sensor cells are excited. The triangle to be considered for this is the one with the point in the eye and the base on the objects. The angle at the eye is smaller as the (same) object gets farther away.
This angle can be increased by optical system like tele-objectives or telescopes and then we feel that the object looks larger.
 

Related to Why do farther away objects appear smaller

1. Why do farther away objects appear smaller?

Objects appear smaller when they are farther away because of the way light travels. Light rays from the object spread out as they travel, making the object's image on our retina smaller.

2. Is it because of perspective?

Yes, perspective is a key factor in why objects appear smaller as they get farther away. The farther an object is, the smaller the angle between our line of sight and the object becomes, resulting in a smaller perceived size.

3. How does the brain interpret the size of distant objects?

Our brain uses visual cues, such as depth perception and comparison with nearby objects, to interpret the size of distant objects. This is why objects next to a distant object may appear larger in comparison, even though they are actually the same size.

4. Does this phenomenon also apply to other senses?

Yes, the concept of objects appearing smaller as they get farther away also applies to other senses. For example, sounds become quieter and less distinct as they travel farther away from their source.

5. Is there a limit to how small an object can appear due to distance?

Yes, there is a limit to how small an object can appear due to distance. This is because there is a minimum size at which our eyes can perceive an object, and as the object gets smaller, it may become too small for us to see it with our naked eye.

Similar threads

Replies
4
Views
673
Replies
4
Views
924
Replies
1
Views
615
  • General Discussion
2
Replies
60
Views
4K
  • Classical Physics
Replies
3
Views
893
Replies
0
Views
650
Replies
19
Views
1K
  • Classical Physics
Replies
5
Views
960
  • Classical Physics
Replies
16
Views
2K
Replies
9
Views
748
Back
Top